Purification of benzoic acid and its derivatives



lto brewing.

This invention relates to processes of separating benzoic acid or itsderivatives from phthalic acid or anhydride and its derivatives. Whenbenzoic acid or its derivatives are my prepared from the correspondinganhydrides, or by a single operation from naphthalene, it is trequentlycontaminated with greater or less amounts of phthalic anhydride oracidl1 tor the benzoic acid. 'lhese solvents tor the most part havelittle or no solvent power tor ,4 phthalic acid and its derivatives.Among the solvents which may be used, particularly with unsubstitutedbenzoic acid and phthalic acid are benzol, toluol, solvent naphtha,chloro form, carbon tetrachloride,- chlorinated hydrocarbons, such asfor example, trichlorethylene, tetrachlorethane and some of thechlorinated residues or sludges produced as a byproduct troin thepurification of aromatic hydrocarbons by selective halogenation, anddescribed in my co-pending applications, Serial No. 86,099, filedFebruary 4t, 1926, and Serial No. 101,561, filed April 12, 1926, ether,parafiin hydrocarbons, esters and other well known organic solvents ofsimilar character. Most of these solvents are lighter than water, andall out them are substantially immiscible All with water.

Accordin to the present invention an aqueous solution oil benzoic andphthalic acids, or the corresponding substituted benzoic and phthalicacids, such as the monodi and tetrachlor substituents, the .nitrosubstituents, homologues, etc., are passed in countercurrent with theorganic solvent. The benzoic acids are largely or completely dissolved bthe organic solvents and practically no phthalic acids are so dissolvedin the case oil the unsubstituted products. Where the solvent is lighterthan water, as is the case with most of the organic solvents, theaqueous solution of the acids is caused to flow downwardtill bill

i A "TUE, PENN$YLWAN, ASSIGNOR CW) THE SELDEN COM- 'lI'lION U13DELAWARE.

$018 ACID AND ITS DERIVATIVES.

Application nled Winter 31%, 119W. serial No. 5. 22735%.

ly in contact with an up-flowing stream of organic solvent. lntimatecontact can be effected by any suitable means such as vigorousagitation, but in general it is undesirable to use an apparatuscompletely filled with line filling bodies, as the capillarity due tothe large surface tends to prevent clean separation ol the solvent andthe remaining water solution oat phthalic acid. After separation thebenzoic acid is recovered, preferably by distilling ofi the solvent, andphthalic acid of high purity is also recovered by boiling d the water,or by any other suitable means.

'lhe process can take place at any suitable temperature, such asroointemperature, or in some cases even at elevated temperatures. Thetemperature, however, will depend on the solvent, as the solubilities ofbenzoic acid and phthalic acid in the various organic solvents arefrequently dependent upon the temperature, and in every case the skilledchemist will choose a temperature which will effect the most rapid andcomplete separation with the particular solvent used. In general,however, l have found that for example with solvents like benzol, inwhich benzoic acid is readily soluble in the cold, the use of roomtempera tures or at most moderate warming is very ef- 'fective, and ofcourse presents advantages in ease and simplicity ol? operation.

In describing the features of the present invention, the process hasbeen described as carried out with a single organic solvent. llt Will beclear to the chemist that the combination olf one or more solvents mayalso be used, and is of course included. in the scope of the invention,and wherever in the specification and claims an organic solvent isreferred to it should be understood that this expression includes also amixture oil organic solvents.

The invention will be described in greater detail in connection with thefollowing examples:

Example 1.

An almost saturated aqueous solution of benzoic acid and phthalic acidcontaining benzoic acid and phthalic acid in the ratio of 85 to ispassed downwardly through a vessel in counter-current to benzol, thebenzol which rises through the acid solution and passes out at the topof the apparatus used dissolves most or all of the benzoic acid, butshows little or no solvent action for the phthalic acid, which latter iscontinuously lltll .iiol in the form of an aqueous solution which issubstantially or largely free from benzoic acid. The benzol may bedistilled off, or the benzoic acid may be precipitated therefrom by anysuitable means. 7 The benz'ol may be recovered and reused. The phthalicacid may be recovered by precipitation with reagents, by boiling off thewater or by concentrating the solution followed by crystal lization, thelatter procedure of course result-' ing in the purest product.

Example 2.

A mixture of orthochlorbenzoic acid and the corresponding 3.chlorphthalic acid dissolved in water to form an almost saturatedsolution is passed downwardly in countercurrent with chloroform, asdescribed in the foregoing example. An excellent separation is effected,and the two products can be recovered from their chloroform and watersolutions respectively as described above.

Example 3.

A mixture of dichlorbenzoic acid and the corresponding dichlorphthalicacid a in aqueous solution is treated as in the foregoing examples usinga mixture of benzol and toluol as the solvent, instead of benzol alone.A good separation is obtained, and the products may be recovered asdescribed.

Example 4.

A mixture of benzoic and phthalic acids in the form of aqueousdispersion is permitted to flow into a treatment vessel together with astream of gasoline. The vessel is provided with partly submerged pipeand nozzle below the submerged end forming the well known air lift ormammoth pump. Any suitable gases, such as air, carbon dioxide, nitrogenor the likeare introduced through the nozzle forming the usual bubblesand lifting the aqueous solution of benzoic and phthalic acids andgasoline in the form of a foam or bubbling liquid. The air lift pipe issuiliciently long so that intimate mixture of the two liquid componentstakes place. The outflowing mixture is then continuously separated intoa gasoline and a water layer in any suitable well known manner and thephthalic acids may be recovered from the water solution while benzoicacids are likewise -recovered from the gasoline solution. The air liftor mammoth pump may besufiiciently long to effect substantially completeseparation in a single passage or the mlxed gasoline .to effectseparation in a stead of gasoline,

and phthalic benzoic dispersion may be passed through'the mammoth pumpseveral times .to effect complete separation. This latter procedurenecessarily, of course, is to a certam extent discontinuous but in manycases presents some advantages in chea er equipment and more perfectseparation. or large outputs, however, it is usually more desirable touse a sufliciently long air lift pi e single passage. nany of thesolvents for EBDZOIC acid may be used singly or in admix- Thisapplication is a continuation in part of my co-pendin application,Serial No. 223,845, filed Octo er 3, 1927.

What is claimed as new is:

.1. A method of separating benzoic acids from the correspondin phthalicacids, which comprises subjecting t e aqueous dispersion of the acids tocontinuous leaching with a current of organic solvents for benzoic acid,separating the solvent from the water and removing benzoic acids fromthe solvent solut on and phthalic acids from the water solution.

2. A method of separating benzoic acids 'from the corresponding phthalicacids, which comprises causing an aqueous dispersion of the two acids tocontact in countercurrent with a stream of organic solvent for thebenzoic acids and separatin the benzoic acids from solution in thesolvent and phthalic acids from the resulting water solutlon.

3. A method of separating benzoic acids fromthe corresponding phthalicacids, which comprises causing an aqueous dispersion of the two acids tomix with a stream of an organic solvent in the lift pipe of a gas liftor mammoth pump, the lift being effected by a gas which does notsubstantially attack benzoic or phthalic acids, separating the effiuentmixture into a water and Organic solvent solutions and separating thebenzoic acids from the organic solvent and the phthalic acids from thewater solution.

4. A method according to claim 3 in which the lift pipe in the mammothpump is so dimensioned with regard to the operating speed that asubstantially complete solution of the benzoic acids in the organicsolvent is effected by a single passage therethru and the effluentmixture is continuously separated into solvent and water streams.

Signed at Pittsburgh, Pennsylvania this 18th day of October, 1927.

ALPHONS o. JAEGER.

